There has been considerable public debate about this issue. One opinion is that there is no more reason to institute resistance management for transgenically produced Bt than there is to institute resistance management for conventional pesticides. Others argue that the use of Bt toxins in transgenic pest-protected crops is fundamentally different from the use of chemical pesticides, for a combination of the following reasons:

  • Insecticides are typically used only when pest populations increase to the point where substantial yield-losses could occur, so refuges are already present. With transgenic Bt crops, the toxin is selecting for resistance all season long, even during weeks when the pest cannot feed on plant parts that affect crop yield, or during years when pest number are too low to cause yield loss.

  • Bt toxins are seen as benign to the environment and public health, and no equally benign replacement product is available.

  • Bt toxins are the active component in Bt spray formulations that have been used sustainably by organic and conventional farmers for many years, and this tool could be lost if transgenic Bt crops are not managed correctly.

Many transgenic pest-protected plants of the future may be protected by novel mechanisms and therefore not compromise the utility of plant protectants that are already being used by farmers. In such cases, the company that produces the plant protectant can be seen as the major party affected by pest evolution of adaptation to the company 's product. However, there could be cases in which a new transgenic pest-protected plant cultivar is produced by transferring a plant protectant that is already in use to another crop species. The new use could increase the risk that pests will involve adaptation to the plant protectant in all uses. An example might be moving a pathogen-resistance gene from tomato into cotton. If the same pathogen is now controlled by this resistance-mechanism in both crops, the intensity of selection for adaptation could be substantially increased. A resistance management program could be developed in such a situation to ensure that adaptation does not evolve at a rate or in a manner that causes environmental, economic, or health problems.

2.9.4 Summary

In light of the above discussion, the committee found that

Evolution of pest strains that can overcome the pest-protection mechanisms of plants can have a number of potential environmental and health impacts.



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